Light
Type Quiz Light travels in a straight line in a ________ medium.
Type Quiz Fill in: angle of incidence equals angle of ________.
The law of reflection states that the angles of incidence and reflection are equal:
Angle of incidence (i) = Angle of reflection (r)
This law of reflection is used in many devices such as:
Examiner Tips and Tricks
When drawing light waves being reflected take care to get the angle about right. If they are slightly out it won't be a problem, but if there is an obvious difference between the angle of incidence and the angle of reflection then you will probably lose a mark.
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| Equipment | Purpose |
|---|---|
| Ray Box | To provide a narrow beam of light that can be easily reflected |
| Protractor | To measure the angles of incidence and reflection |
| Sheet of Paper | To mark the lines indicating the incident and reflected rays |
| Pencil | To draw the incident and reflected ray lines onto the paper |
| Ruler | To draw the incident and reflected ray lines onto the paper |
| Plane mirror | To reflect the light beam |
Example results table:
| Angle of incidence, i (°) | Angle of reflection, r (°) |
|---|---|
| 10 | |
| 30 | |
| 45 | |
| 80 |
The law of reflection states: i = r
Systematic errors
Random errors
Type Quiz Light travels in a straight line in a ________ medium.
Type Quiz Light travels in a straight line in a ________ medium.
Examiner Tips and Tricks
Practice drawing refraction diagrams as much as you can! It's very important to remember which way the light bends when it crosses a boundary: As the light enters the block it bends towards the normal line. Remember: Enters Towards. When it leaves the block it bends away from the normal line. Remember: Leaves Away.
You only need to know about light passing through the boundaries between two media.
Type Quiz Snell’s law: n1 sin θ1 = n2 sin θ__
Type Quiz Complete: n = __ / v
Type Quiz Snell’s law: n1 sin θ1 = n2 sin θ__
Type Quiz Complete: n = __ / v
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Type Quiz Snell’s law: n1 sin θ1 = n2 sin θ__
Type Quiz Complete: n = __ / v
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A ray of light enters a glass block of refractive index 1.53 making an angle of 15° with the normal before entering the block. Calculate the angle it makes with the normal after it enters the glass block.
Answer:
Step 1: List the known quantities
Step 2: Write the equation for refractive index in terms of the ratio of angles
n = sin(i) / sin(r)
Step 3: Rearrange the equation and calculate sin(r)
sin(r) = sin(i) / n
sin(r) = sin(15) / 1.53
sin(r) = 0.1692
Step 4: Find the angle of refraction (r) by using the inverse sin function
r = sin⁻¹(0.1692)
r = 9.7 = 10°
Examiner Tips and Tricks
n = sin(i) / sin(r) is also known as Snell's law but you do not need to know this for your exam.
Important: (sin i) / (sin r) is not the same as (i / r). Incorrectly cancelling the sin terms is a very common mistake!
When calculating the value of i or r start by calculating the value of sin i or sin r. You can then use the inverse sin function (sin⁻¹) on most calculators by pressing 'shift' then 'sine') to find the angle.
One way to remember which way around i and r are in the fraction is remembering that 'i' comes before 'r' in the alphabet, and therefore is on the top of the fraction (whilst r is on the bottom).
Type Quiz Critical angle: sin c = __/n
Type Quiz Critical angle: sin c = __/n
Type Quiz Critical angle: sin c = __/n
The colourful pattern observed on a CD is a result of thin film interference. Other examples of thin film interference include:
Type Quiz Critical angle: sin c = __/n
Total internal reflection is used to reflect light along optical fibres, meaning they can be used for:
Examiner Tips and Tricks
If asked to name the phenomena make sure you give the whole name - total internal reflection.
Remember: total internal reflection occurs when light travels from a denser material to less dense material and ALL of the light is reflected.
If asked to give an example of a use of total internal reflection, first state the name of the object that causes the reflection (e.g. a right-angled prism) and then name the device in which it is used (e.g. a periscope).
Type Quiz Light travels in a straight line in a ________ medium.
Type Quiz Light travels in a straight line in a ________ medium.
Examiner Tips and Tricks
To remember which lens is converging or diverging, think of the following: Convex lens = Converging. You need to be able to describe how the lenses affect the light rays.
The three main rules for constructing ray diagrams are as follows:
Object placed beyond 2f
When an object is placed beyond 2f (to the left of the lens), the image that forms (to the right of the lens) will have the following properties:
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The image that forms will have the following properties:
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Examiner Tips and Tricks
To remember the colours of the visible spectrum you could remember either:
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